Area Forecast Discussion
Issued by NWS Seattle/Tacoma, WA
Issued by NWS Seattle/Tacoma, WA
631 FXUS66 KSEW 282014 AFDSEW Area Forecast Discussion National Weather Service Seattle WA 114 PM PDT Tue May 28 2024 .SYNOPSIS...Rain showers will continue to spread inland today as a frontal system moves across Washington. Convergence zone activity east of the Puget Sound will continue through the evening with continued shower activity on Wednesday. A shortwave ridge and surface high to the south will bring warmer and drier conditions for the rest of the week. A series of systems will cross the Pacific Northwest over the weekend and into early next week, bringing more rounds of wet weather. && .SHORT TERM /TONIGHT THROUGH FRIDAY/...Stratiform rain spreading inland will continue to destabilize this afternoon and transition to showers. Skies will stay mostly cloudy today, limiting high temperatures to the 50s for most areas. While mean model instability is fairly limited at 100 J/kg or less, a lightning strike cannot be ruled out this afternoon. Confidence is high that convergence zone activity will form this evening over the Puget Sound which will slowly propagate eastward, lingering through the early morning hours on Wednesday. Short range ensembles keep most of the PSCZ shower activity north of Stevens Pass Highway before dissipating. More post-frontal showers will spread inland on Wednesday as an upper level trough axis passes overhead, and models continue to show another round of PSCZ showers developing in the evening. A few lightning strikes are possible once again on Wednesday afternoon in any stronger showers that develop, with slightly more instability available. Temperatures will peak a couple degrees higher on Wednesday, closer to 60 degrees for most areas. High pressure will build inland on Thursday and Friday, allowing conditions to dry out. Any lingering showers will be limited to the northern Olympic Peninsula and North Cascades. Temperatures will warm towards the end of the week, reaching a degree or two below normal by Friday in the mid to upper 60s for most lowland locations. .LONG TERM /SATURDAY THROUGH TUESDAY/...Ensembles show good agreement that cooler and wetter conditions will return throughout the long term. A weak shortwave trough is on track to move across the region on Saturday, cooling temperatures off a few degrees and bringing in scattered showers. The region will have little time to dry out with a series of deeper storm systems following close behind. Long range ensembles continue to show much wetter conditions entering the region Sunday through Tuesday, especially over the western Olympic Peninsula and Cascades, where up to 4 inches of rainfall is currently forecast to fall over the span of three days. However, models continue to show a wide range of possible solutions with GFS precipitation amounts nearly double that of the ECWMF. Uncertainty remains in terms of rainfall totals and the placement of heaviest rainfall through the period. Temperatures will return to near- normal with highs in the low to mid 60s through the weekend and into early next week. Lindeman && .AVIATION...An upper level trough will pass through today with a weakening cool front/surface trough. Flow aloft is southwesterly and will transition to west/northwesterly once the trough passes early Wednesday. Light rain bands continue with the low feature passing through western Washington this afternoon. Some of the showers have been able to knock visibilities and ceilings down to IFR briefly at times. Otherwise, ceilings remain MVFR and improvement to VFR is still expected late this afternoon and evening. However MVFR ceilings will return for Wednesday morning for the majority of the terminals. Convergence zone activity remains possible, which if one does form, winds will flip to the west northwest from KPAE, south to potentially KSEA. The time span for this wind flip is expected to last roughly 3 to 5 hours, from 21-22Z through around 04-05Z. Variable winds from other directions are possible during this time span. Wind speeds are expected to remain around 5 to 10 kt, but a couple gusts to 20 kt cannot be ruled out. KSEA...Mix of MVFR/VFR ceilings this afternoon improving to VFR as shower activity ends. MVFR ceilings will return tomorrow morning. Possible convergence zone activity to the north may bring variable winds from 23Z-05Z (flipping from southwest to north & east, and then back to southwest). Potential exists for gusts out of these variable directions. Otherwise winds outside of this window will be out of the southwest at 8 to 12 kt. HPR && .MARINE...An upper level trough is swinging a front through this afternoon, with shower activity over much of the waters. Increase in onshore flow will follow the trough. The push is strong enough for gusty winds of 15 to 25 kt in the Central/East Strait of Juan de Fuca. The small craft advisory will remain in effect for the rest of the day. A similar push is expected Wednesday night into Thursday. Otherwise winds will remain light and predominately onshore for the forecast period. Waves will remain at 4 to 6 ft in the outer coastal waters, with a system early next week bringing waves up to 6 to 8 ft. HPR && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory from 2 PM this afternoon to 2 AM PDT Wednesday for Central U.S. Waters Strait Of Juan De Fuca- East Entrance U.S. Waters Strait Of Juan De Fuca. && $$